Hi-Fi News - May 2016

PREAMPLIFIER
Valve preamplifier
Made by: Audio Research Corp, Minnesota, USA
Supplied by: Absolute Sounds Ltd
Telephone: 0208 971 3909
Web: www.audioresearch.com; www.absolutesounds.com
Price: £12,000
Audio Research Reference 6
Replacing the long-serving Reference 5, and coming in below the £30k Reference 10,
Audio Research’s Reference 6 preamp heralds a new phase in the company’s evolution
Review: Ken Kessler Lab: Paul Miller
T
wenty sixteen is the 21st
anniversary of the Audio Research
Reference Series, and in that
period, there have been seven line
stage preamps. As a reviewer who takes
the term ‘reference’ to mean a standard by
which to judge other components, I have
been wedded to the range since 2009’s
REF 5. With the Reference 6, a new level
of performance has been attained at the
£12,000 level, the lower tier of the line.
Because Audio Research developed the
Reference range into a family, rather than
just a flagship preamp and power amp
(plus phono stages and DACs along the
way), the company added stereo and mono
power amps of varying outputs and, of late,
at least two line-stage preamps. The singlechassis REF 6 is the less costly of the two:
the company’s ‘ultimate’ remains the REF
10 two-box affair [HFN Mar ’13], at three
times the cost.
Because the ’6 post-dates the ’10, the
gap is closer than one might think, and
the Law of Diminishing Returns comes into
play. Yes, the REF 10 is the ‘daddy’, but the
’6 is not a case of glory through nepotism.
Rather, it is to the ’10 what Porsche’s
Cayman is to the 911, and if you’re a car
nut, you’ll know that the analogy doesn’t
mean ‘cheaper’ – it means ‘less expensive’.
21ST CENTURY RETRO
One of the first products to appear under
the aegis of ARC boss Mike Tsecouras
– a dyed-in-the-wool tube-lovin’ audio
casualty – the REF 6 had to replace one
of the company’s most successful linestages. More importantly, it had a stylistic/
aesthetic role to play because – after the
company was acquired by Italians – the
new G-Series [HFN Jan ’15] introduced a
fresh look.
So, starting with the fascia, the REF 6
is as much a break from tradition as it is a
continuance. Re-read that: this is no wild
RIGHT: The vacuum tube audio stage employs
six 6H30 triode tubes (three per channel)
together with another 6H30 and 6550WE beam
tetrode for regulation in the power supply
30 | www.hifinews.co.uk | MAY 2016
departure from a design language dating
back to the early 1970s. The handles are
still there, the laboratory-look remains, but
the designers performed a visual segue
that ranks alongside the new Mini, so you
know instantly that this is an ARC preamp,
but the look is 21st century retro.
Far more important are the
improvements over the REF 5SE. It remains
a line stage, as ARC has kept phono
stages as components on their own. Says
Tsecouras, ‘The combined lessons learned
from our flagship REF 10 line stage, and
those from our recently released SE power
amps became the starting point for the
complete redesign of the REF 6 line stage.’
ARC’s continued support of a trickle-down
philosophy explains why the new ’6 is
closer to the earlier ’10. For openers, the
REF 6 has a redesigned valve preamp stage
using six 6H30 triodes instead of four 6H30
tubes. The company increased the tube
count to provide more linear gain [see PM’s
Lab Report, p33], in the quest for a more
dynamic and precise sound.
I was told that by fitting a larger R-core
power transformer, ARC has reduced the
impedance of the REF 6’s power supply,
which now boasts a lower impedance by
using improved decoupling capacitors
specially developed for the REF 6.
Also devised specifically for the REF 6
are the output coupling caps, ‘to allow
the new circuitry’s linearity to be revealed,
in both tonality and in image specificity’.
That’s a mildly vague statement, not easily
ascertained by mere listening, but it helps
perhaps to define the sensation one hears
when moving from ’5 to ’6 with levels
matched: the ’6 has an authority that
reminded me of the ARC Anniversary [HFN
Apr ’11] and the ’10, with the external
power supplies.
CASEWORK MAKEOVER
Back to the externals. The outputs remain
the same, with two sets of main outputs
and one for record out, in both singleended and balanced XLR modes, but the
input layout has changed, while an eighth
has been added. Instead
of the inputs being
labelled, with sockets
grouped in vertical pairs
of XLR-plus-single-ended,
they are arrayed as four
balanced inputs and four
single-ended inputs. All
are labelled only as ‘Bal
1, 2…’, etc, and ‘SE 1, 2…’, etc. Specific
labelling of each is up to the user, via the
new digital control section.
This makeover also added heavier,
shaped side panels, which make the
unit look butch, while providing more
isolation to feedback from acoustic and
mechanically induced noises. The luxury
feel has been enhanced by the use of
knobs and push buttons from machined
aluminium, combined with new optical
encoders. This feel is also evident in the
all-metal remote [see p33], adding to the
sense of opulence.
For once, the owner’s manual is
essential reading, for when I switched
sources for the first time, I got nothing out
of a single-ended input. Scrolling through
the menu, I found a setting called ‘Volume
Reset’, fiddled with it,
and out came the sound
because that option
determines how the REF
6 remembers levels…
or not.
This has created
a change to the row
of buttons below the
display. The REF 5SE’s processor and
balanced/single-ended buttons have
been replaced with ‘Menu’ and ‘Enter’.
The processor mode is now in the menu,
while the balanced/SE mode selector isn’t
needed as the remote contains buttons
for all eight inputs. The rest remain as per
the ’5SE for power on, mono, invert and
mute. Other functions in the menu include
‘Brass and strings
had a tube-y
sweetness I could
never give up’
GENERATION GAME
Careful evolution best describes the path of ARC’s single-chassis Reference
preamps, which started with the REF 1 in 1995, notable for its resemblance to
‘classic’ ARC preamps with its row of knobs above toggles, between handles.
Its gain was all-tube, with eight inputs, but with full microprocessor control
of volume, balance, record and input selection. It also featured fully regulated
power supplies, dedicated analogue and logic transformers and audiophile-grade
components throughout. The REF 2 from 1998 looked the same and allowed ’1s
to be upgraded to ’2s. A unity gain stage was added, as was tube regulation. The
REF 3 of 2004 was a full re-design, now featuring a fluorescent display and menu
that replaced many controls. With the REF 5 of 2009, the circuit design was
revised again, now fully balanced and operating in pure Class-A triode mode, but
the basic look remained the same. Its valve complement comprised four 6H30s
in the analogue stage, with a 6550 and a 6H30 in the power supply.
ABOVE: Like the REF 5, the ’6 places a rotary
control to either side of the fluorescent display
for input select and level, with six function
buttons below; remote takes care of the rest
a mode where the REF 6 automatically
goes to sleep according to user preference,
one for setting display brightness, balance,
and displaying hours of valve usage.
The processor setting assigns unity gain,
or ‘pass through’, to one of the eight
inputs should the user want that source
integrated into a system with a secondary
device, such as a surround sound processor.
CHILLINGLY REAL
I quickly discovered that, auditioned
with REF 75SE power amps and Wilson
Alexias [HFN Mar ’13], the REF 6 needs
the recommended 300 hours’ burn-in to
approach its best, with at least 20 minutes
warm-up from cold. The review sample
arrived with 250 hours on it, so – after
an initial burst – I let it run-in another 50
hours over a weekend. It was worth it.
Knowing intimately the nuances of
Eleanor McEvoy’s Naked [Moscodisc/Diverse
DIV 052LP], I wasn’t prepared for an even
more gut-wrenching reaction to her most
emotional moments. And this is an LP
where emotion oozes from every squiggle
in the groove. While the ’5SE had charmed
me for years, the ’6 found a way to open
up the sound even more.
I can liken it only to a change from
one grade of cable to the next level up,
whether Crystal or Nordost or Transparent,
when the gains to voicing are genuinely
and easily discernible. Perhaps I’m
privileged in having heard McEvoy live
more than once, and as close to her as I
sit to my speakers. The resultant portrayal
was chilling, almost supernatural rather
than merely authentic. That may sound like
mere exaggeration, but such was the
MAY 2016 | www.hifinews.co.uk | 31
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Hi-Fi News Review September ‘15
LAB
REPORT
AUDIO RESEARCH REFERENCE 6
ABOVE: Line-level preamp offers four balanced (on XLR) and four single-ended (on
RCA) inputs with pairs of XLR/RCA outputs (plus rec out). RS232 services automation
surprise that I was taken aback.
When she thumped her acoustic
guitar, the sound was so unsullied
that I ran to find a facsimile (OK, my
concert-sized Carvalho ukulele) just
to hear the real sound of tapping
on a wooden enclosure. A cigar box
would have served. Regardless, it
was a real wood tonality.
AND BASS QUALITY?
Readers know I’m no bass fetishist.
But turning to the pre-disco/funk
classics on both CD and vinyl – the
Detroit Emeralds’ ‘Feel The Need’
[Greatest Hits, Westbound CDSEWD
119, CD, and Feel The Need Atlantic
K50372, LP] and ‘Rock The Boat’ by
the Hues Corporation [The Very Best
Of The Hues Corporation, Camden
74321 603422, CD, and Freedom
For The Stallion RCA APL 1-0323, LP]
– I discovered what may be the most
staggering gain of all.
Let’s back up a mo’. The McEvoy
experience wasn’t just about
transparency. There was a fullyformed soundstage, the threedimensionality of a standard I have
always expected of Audio Research.
Tonal neutrality was, to my ears,
absolute, with no ear-jarring
anomalies. After that one track,
I was ready to sign off the ’6 as a
target of true lustworthiness. But
the lean, mainly-unplugged McEvoy
LP is no feast for headbangers, nor
bass junkies, for it’s a test primarily
of neutrality and presence.
So far, the REF 6 had ticked
every box bar transient attack and
bass in its various measures, but
only because it hadn’t been so
challenged. Both the disco cuts
listed featured heavy orchestration,
massed vocals and wall-of-sound
impact of near-Spectorian majesty.
Via the REF 6 preamp, the brass
and strings possessed the tube-y
sweetness that I could never give
up, no matter how much I respect
solid-state achievements from that
genre’s maestri.
Wham! The rolling lower octaves
of both of those early 1970s
treasures added a foundation I had
never heard in my system. Extension,
weight, sheer mass – the bass was
as profound as I had heard from
far larger systems than my Wilson
Alexias. And the attack? The brass
was so sharp, so punchy that I
almost wished I understood square
waves and oscilloscopes…
Although I’d heard the REF 6
four times before using it in my
own system, I was not completely
prepared for the leap in sound
quality. It became evident mainly
because I could run it side-byside with a ’5SE. The gains are as
extreme as those between two
generations of Ferraris. They are
vivid and so readily apparent as to
defy expectations. Hell, it’s so good
that, if you don’t have £30k for the
REF 10, then you won’t lose sleep
‘settling’ for the REF 6.
Six years on from the launch of Audio Research’s REF 5 [HFN Oct
’10], the upgraded and restyled REF 6 still bears many of the
key hallmarks of its forebear. The balanced outputs are capable
of delivering over 50Vrms from a 300ohm source impedance,
increasing to 455ohm at 20Hz, and while this preamp features
an additional pair of 6H30P Sovtech double triodes in its line
stage the overall gain (balanced in/out) is unchanged at +12dB
as is the A-wtd S/N ratio of 96.5dB (re. 0dBV). Distortion is well
within ARC’s broad 0.01% specification but is now just half that
incurred by the REF 5, at typically 0.001% from 20Hz-20kHz
[see Graph 2, below]. Versus output level, distortion increases
from just 0.0004% at 0.5V to 0.001% at 2V and 0.005% at 10V
– demonstrating that tube amps needn’t be coloured...
Like the REF 5, however, the REF 6’s response varies with
volume setting [see Graph 1] suggesting that ARC’s buffering of
this circuit has not changed. In practice, the REF 6 achieves its
flattest response of –0.01dB/20kHz and –0.35dB/100kHz at full
volume (+12dB gain or 103 on the display) but with its most
aggressive treble roll-off of –1dB/20kHz and –8.6dB/100kHz at
+6dB gain (86 on the display). As the volume is reduced still
further the treble slowly picks up to achieve –0.6dB/20kHz and
–7.0dB/100kHz at 0dB gain (61 on the display), –0.2dB/20kHz
and –3.2dB/100kHz at –6dB gain (41) before reaching
–0.1dB/20kHz and –2.0dB/100kHz at –12dB gain (35 on the
display). Finally, stereo separation is improved at >80dB (20Hz20kHz) compared to >65dB for the REF 5, just as the channel
balance is now tightly trimmed to <0.02dB. Readers may
view a full QC Suite test report for the Audio Research REF 6
preamplifier by navigating to www.hifinews.co.uk and clicking
on the red ‘download’ button. PM
ABOVE: Frequency resp. vs. volume (vol display = 103,
black; 86, black dashed; 61, red; 41, blue; 35, green)
HI-FI NEWS VERDICT
Audio Research has never put a
foot wrong with its Reference
models. I’ve played with most,
and must admit that some stand
out more than others. The REF
6, I believe, will join the ranks
of the revered SP6 and SP-10.
We’ve been subjected to so much
hyperbole (mea culpa) for so
long that superlatives lose their
impact. But here, ‘masterpiece’
doesn’t come close to describing
what ARC hath wrought.
Sound Quality: 91%
0
-
-
-
-
-
-
-
- 100
ABOVE: Distortion versus extended frequency from
5Hz-40kHz at 0dBV (left, black; right, red)
HI-FI NEWS SPECIFICATIONS
Maximum output (<1% THD, 47kohm)
55Vrms (Balanced)
Maximum input level (<1% THD)
>10Vrms (Balanced)
Output impedance (20Hz–20kHz)
303-457ohm (Balanced)
Frequency response (20Hz–100kHz)
+0.01dB to –8.6dB (re. 0dBV)
Input sensitivity
240mV (Balanced)
A-wtd S/N ratio (re. 0dBV)
96.5dB
Distortion (20Hz-20kHz re. 0dBV)
0.0006–0.0009%
Power consumption
131W (4W standby)
Dimensions (WHD) / Weight
480x198x419mm / 16.6kg
MAY 2016 | www.hifinews.co.uk | 33